A low complexity MMSE multiuser detector for DS-CDMA

A novel, low complexity, reduced rank multiuser detector (MUD) for DS-CDMA is presented. The solution is derived for the general case of an asynchronous DS-CDMA system in frequency selective multipath. The joint MUD solution is shown to be equivalent to a bank of parallel, single user detectors, previously shown only for synchronous users. The algorithm is implemented in low complexity form, using the efficient correlations subtractive architecture of the reduced rank multistage Wiener filter (CSA-MWF). The reduced rank algorithm is not based on an eigen-decomposition, which requires the signal subspace rank to be greater than or equal to the number of signals present in the system, and is shown to be nearly independent of the number of signals. It is shown that the joint and parallel CSA-MWF implementations perform identically to the full rank MMSE MUD and approaches single user, full rank performance at significantly reduced ranks. Bit error rate (BER) performance, as a function of rank, signal-to-noise ratio, number of users, code type and synchronism among the codes, is analyzed.